The present invention relates generally to fuel delivery systems for engines, especially aircraft gas turbine engines, and, more particularly, to a dual function rapid shutdown and ecology system for such fuel delivery systems, which performs its function upon engine shutdown.
Two of the functions provided by the fuel control system of a gas turbine engine are fuel shutoff/turn-on and ecology fuel management. The first function, fuel shutoff/turn-on, may be manually commanded from the control system (for instance, by the pilot for aircraft applications), or it may be triggered automatically through an overspeed detection system provided by the engine""s electronic control. In the later case, the response of the system must be extremely fast so as to limit the engine speed excursions above the normal operating range.
A second function of the fuel control system is ecology management, and requires that the fuel in the manifold be disposed of properly during shutdown and not be allowed to drain into the engine where it will vaporize and/or smoke when in contact with the still-hot combustion chamber, thereby creating atmospheric pollution. Also, after any type of shutdown, it is necessary that fuel remaining in the engine fuel manifold be removed rapidly to keep it from puddling. Fuel left in the manifold can cause hot starts upon subsequent engine operation and will also coke the engine""s fuel nozzles, a condition which hinders nozzle performance, leading to premature failure.
An examination of prior art shows that there have been many and varied attempts to address one or both of the aforementioned fuel control system functions. Of particular interest in this regard are the following references and examples:
U.S. Pat. No. 4,206,595 discloses a system to collect fuel left over in the fuel manifold upon engine shutdown and reintroduce it on the next engine start. The system uses two check valves, two springs and two pistons to accomplish this function.
U.S. Pat. No. 5,809,771 teaches a system which uses flow divider differential pressure to remove fuel from the fuel manifold upon engine shut-down and which temporarily stores the fuel until the engine is subsequently restarted.
U.S. Pat. No. 6,195,978 B1, assigned to the assignee of this application, involves a system whereby fuel flow is reversed upon engine shut-off by adding one valve to the main fuel control and modifying the main fuel control pressurizing valve to include a pressure switch function. The invention is also directed toward gas turbine engines that include both primary and secondary manifold systems.
U.S. patent application Ser. No. 09/361,932, also assigned to the assignee of this application, discloses a fuel divider and ecology system adapted for engines requiring three discrete fuel manifolds. The ecology function is accomplished using one single chamber staged valve and modifying the main fuel control pressurizing valve to include a pressure switching function.
Various other prior art fuel systems have addressed fuel shutoff/turn-on concerns as well as ecology issues and have introduced various other techniques in an effort to control both problems. Examples include: draining fuel overboard after engine shutdown, blowing unburned fuel into and through the engine at shutdown, and draining unburned fuel into a tank that must be manually emptied.
None of the above cited prior art provide a single, simple, module that accomplishes the dual functions of rapid shutoff (or turn on) of fuel flow as well as ecology management.
The present invention accomplishes the dual function of rapid shutdown and ecology management in a single module operated by a single electromagnetic solenoid valve. In one aspect of the present invention, a cylindrically shaped valve body is provided to house a large spring loaded piston member, which when extended due to pressure differentials caused by actuation of the solenoid valve, provides sufficient volume to accommodate all fuel left over in the fuel manifold and distribution system at shutdown. Simultaneously, a secondary small piston member, which is housed internal to the underside of the large piston member, also actuates causing all fuel being delivered to the engine combustion chamber to be bypassed back to pump inlet.
In another aspect of the present invention, separate cylindrically shaped valve bodies are provided to house the large spring loaded piston member and the small piston member. This alternate embodiment is intended for use on fuel control systems employing low pressure differentials along various stages of the fuel control system manifold. The large spring loaded piston member extends at low pressure differentials caused by actuation of the solenoid valve, and provides sufficient volume to accommodate all fuel left over in the fuel manifold and distribution system at shutdown. A small accumulator, or alternatively a check valve, is provided to accommodate a small amount of fuel displaced upon actuation of the large piston member. Simultaneously, with actuation of the solenoid valve, the remotely located small piston member, also actuates causing all fuel being delivered to the engine combustion chamber to be bypassed back to pump inlet.
These and other objects, features and advantages of the present invention, are specifically set forth in, or will become apparent from, the following detailed description of embodiments of the invention when read in conjunction with the accompanying drawings.